The present invention relates to an arrangement for detecting the angle of rotation of a rotatable element as generically defined by the preamble to claim 1 and to a corresponding method as generically defined by the preamble to claim 9.
Arrangements of this kind, with which a contactless detection of the angle of rotation can be performed, are known for instance from Published, Nonexamined German Patent Application DE-OS 195 43 562. In these arrangements, a magnet is connected to the rotatable shaft whose angular position is to be ascertained. The magnetic field, which varies with the angle of rotation of the shaft, is measured with the aid of two sensor elements, These sensor elements are either two Hall sensor elements, which are rotated by an angle of 90xc2x0 relative to one another, or two magnetoresistive sensor elements, which are rotated by 45xc2x0 relative to one another. These sensor elements are supplied with alternating voltage signals that are phase-shifted relative to one another in a suitable way. The superposition of the output signals of the sensor elements produces a signal course which is representative for the angular position. The arrangements for contactless detection of the sensor element that are described in this reference each have two identical sensor elements. This can have disadvantages, since Hall sensors for instance have a high temperature dependency and a high stress dependency. Magnetoresistive sensor elements, conversely, have more favorable properties with regard to the temperature and stress dependency, and are less temperature- and stress-dependent than Hall sensors, but they do have the disadvantage that because of the physical effect, an angular range of only 180xc2x0 can be detected unambiguously, Such an angular range is too small for detecting the position of the camshaft of an internal combustion engine, for instance, or in steering wheel angle measuring methods.
From German Patent Disclosure DE-P 197 22 016, an arrangement for contactless detection of the angle of rotation of a rotatable element is known, in which, utilizing magnetically variable properties of a sensor arrangement with at least two sensor elements, a magnetic field intensity generated or varied by the rotatable element is detected in an evaluation circuit and used to ascertain the rotary position; one sensor element functions utilizing the magnetoresistive effect, and the other sensor element functions using the Hall effect, and the signals output by the two sensor elements are combined with one another. Combining magnetoresistive sensors and sensor elements proves in practice to be very complicated and expensive.
The object of the present invention is to create an arrangement and a method for detecting the angle of rotation with which the largest possible angular range, and in particular 0xc2x0-360xc2x0, can be detected unambiguously at low effort and expense.
This object is attained by an arrangement having the characteristics of claim 1 and by a method having the characteristics of claim 9.
According to the invention, it is now possible for the first time to use a magnetoresistive sensor arrangement for unambiguous determination of an angle between 0xc2x0 and 360xc2x0. In contrast to sensor arrangements of the prior art, no additional Hall sensors are needed here. As a result, the expense for furnishing an arrangement for detecting an angle of rotation are reduced. Advantageous applications arise for instance in detecting the position of a camshaft of an internal combustion engine. The present invention can also be advantageously employed in steering wheel angle measuring methods, since the increase in the nonambiguity range to 360xc2x0 that is achieved over conventional methods leads to an increase in the tolerance limits of the entire system.
Advantageous features of the invention are the subject of the dependent claims.
In one preferred feature, the sensor arrangement has a number of magnetoresistive elements, which are At interconnected to form at least two bridge circuits, in particular Wheatstone bridges, of which one bridge furnishes a signal associated with the cosine of the angle of the first magnetic field Bext to be detected with respect to a reference direction, and a further bridge furnishes a signal associated with the sine of this angle. On the basis of these linearly independent signals, signal evaluation is simple to perform.
Expediently, the magnetoresistive elements are embodied as AMR gauge strips. Such gauge strips can be applied to a substrate in a suitable orientation in a relatively simple and inexpensive way.
It is preferred that the current flow directions in each of two magnetoresistive elements associated with one bridge branch of the bridge circuits extend perpendicular to one another.
Expediently, the bridge circuits are rotated, in particular by an angle of 45xc2x0, relative to one another. With this arrangement, sine and cosine can be extracted in a simple way.
It is preferred that the magnetic auxiliary field BH has different directions in the bridge circuits, and these directions in particular form an angle of 45xc2x0.
Expediently, the magnetoresistive elements are embodied in meander form. As a result of this provision, higher sensor signals that are simpler to evaluate can be attained.
It is preferred that the magnetic auxiliary field BH be generated by means of a planar coil, which by means of a nonconductive intermediate layer is disposed in electrically insulated fashion with respect to the magnetoresistive elements. With such a coil, the expense for wiring is relatively low; moreover, both the amount and direction of the auxiliary field BH are adjustable in a desired way.
According to a preferred embodiment of the method of the invention, the correlation is performed by means of a range function F taking the form
F=((0xc2x0xe2x89xa6xcex1AMR180xe2x89xa6f(xcex11,xcex12)) AND ((xcex4Ucos greater than S) OR ((xcex4Usin less than xe2x88x92S) AND (|xcex4Ucos| less than S)))) OR ((f(xcex11,xcex12) less than xcex1AMR180xe2x89xa6180xc2x0) AND ((xcex4Ucos greater than S) OR ((xcex4Usin greater than S) AND (|xcex4Ucos| less than S)))),
in which xcex1AMR180 represents an angle of rotation detected with a 180xc2x0 nonambiguity range, without the application of the auxiliary field BH; S represents an adjustable significance threshold; xcex4Ucos and xcex4Usin, represent the angle-dependent variation signals of the sensor arrangement; and f(xcex11,xcex12) represents an addition or subtraction function of the angular orientations of the bridge circuits or of the auxiliary field at the site of the applicable bridge circuits with respect to a reference direction. In this way, a method that can be performed inexpensively in terms of computation is made available for unambiguous determination of an angle of rotation over an angular range of 360xc2x0. The form of the range function depends on the direction of the magnetic auxiliary field BH in the respective bridge circuits. A distinction can be made between the angular ranges of 0xe2x89xa6xcex1xe2x89xa6180xc2x0 and 180xc2x0xe2x89xa6xcex1xe2x89xa6360xc2x0 by using a magnetic auxiliary field BH for arbitrary directions of the auxiliary field BH; care must be taken to assure that the direction of BH at the site of the bridge circuit 1 differs from that at the site of the bridge circuit 11. It is advantageous in particular if the BH directions differ by 45xc2x0.
In an especially preferred embodiment of the method of the invention, f(xcex11,xcex12) is a function taking the form xcex11+xcex12. For the case where the auxiliary field BH is applied in the direction xcex1=90xc2x0 at the site of the bridge circuit 1 and in the direction xcex1=45xc2x0 at the site of the bridge circuit 11, the resultant range function is for instance
xe2x80x83F=((0xc2x0xe2x89xa6xcex1AMR180xe2x89xa6f(xcex11,xcex12)) AND ((xcex4Ucos greater than S) OR ((xcex4Usin less than xe2x88x92S) AND (|xcex4Ucos| less than S)))) OR ((135xc2x0 less than xcex1AMR180xe2x89xa6180xc2x0) AND ((xcex4Ucos greater than S) OR ((xcex4Usin greater than S) AND (|xcex4Ucos| less than S)))).
In a further especially preferred embodiment of the method of the invention, f(xcex11,xcex12) is a function taking the form |a1-a2|. For the case where the magnetic auxiliary field BH has a direction of xcex1=90xc2x0 at the site of the bridge circuit 1 and a direction of xcex1=135xc2x0 at the bridge circuit 1, the resultant range function is for instance
F=((0xc2x0xe2x89xa6xcex1AMR180xe2x89xa6f(xcex11,xcex12)) AND ((xcex4Ucos greater than S) OR ((xcex4Usin less than xe2x88x92S) AND (|xcex4Ucos| less than S)))) OR ((45xc2x0 less than xcex1AMR180xe2x89xa6180xc2x0) AND ((xcex4Ucos greater than S) OR ((xcex4Usin greater than S) AND (|xcex4Ucos| less than S)))).